Generally, in order to write a mask (may be called a reticle also) that is used in manufacturing a semiconductor integrated circuit, it is necessary to provide, on the surface of a quartz plate or the like which will serve as a substrate of the mask, a chromium film or the like that shields exposure light in a pattern corresponding to an intended circuit pattern. This chromium film or the like is patterned by exposure and the general technique of exposing a pattern by lithography is known as electron-beam lithography that uses an electron beam. As is readily understood from the fact that such lithography is called electron-beam direct lithography or drawing, the lithography is carried out by moving a narrowed electron beam along the pattern and, as a result, is executed by a system that is normally called an EB lithography system.
In a general exposure system using ultraviolet light, a mask is used which has a size that is equal to four or five times a circuit pattern size of a semiconductor chip to be manufactured. On the other hand, there is also an exposure method that uses a mask having the same size as that of a circuit pattern of a semiconductor chip (hereinafter, this mask will be referred to as a proximity mask). This is called proximity exposure and may be called, for example, LEEPL (first letters of Low Energy E-Beam Proximity Lithography), proximity X-ray exposure, and so on. Further, in this exposure technique, the proximity mask is disposed immediately above or proximate to a wafer. The exposure is carried out by irradiating an electron beam in the case of the LEEPL or an X-ray in the case of the proximity X-ray exposure through the mask.
On the other hand, a mask writing system has been also manufactured and sold, that is based on a technique that performs pattern lithography (i.e. exposing in a pattern onto a mask substrate applied with a resist) by the use of laser light in the ultraviolet region (hereinafter abbreviated as ultraviolet laser light), instead of the electron beam (this system is sometimes called a laser-beam lithography system). There are two types in structure with respect to this system. One is such that the pattern lithography is performed on the mask substrate by applying thereto ultraviolet laser light in the form of one beam or divided into a plurality of beams. As the other structure, use is made of reflector display elements that are composed of a large number of micromirrors arranged two-dimensionally and that are called digital micromirror devices or the like. The pattern lithography is performed on the mask substrate by irradiating ultraviolet laser light onto the reflector display elements and by controlling a pattern of reflected light. This laser-beam lithography system can expose a partial pattern of a circuit pattern at a time and therefore has a feature that the processing speed is fast, as known in the art. Description is given about this, for example, in the July 2001 issue of Electronic Journal, pp. 140-142.